Got the Lydia several years ago and with a broken cam-stack and cam-stack gear I just put it in the back
MoMA collection; a true exercise in Functional Design.
So it has the standard cracked cam-stack and cam-stack gear, after talking to a fellow SM enthusiast who used hers for straight stitch only I decided to make mine into a straight stitch too.
The entire cam mechanism is a module that loads from the hand wheel end of the machine so it is not too difficult to remove the broken parts.
The fix was to drill thru the center pin and tap the hole all the way thru. With a screw on the back side the spring is held fast.